The present invention relates to a new and improved construction of installation for the mechanical-biological purification of waste water or sewage incorporating at least one biological stage and one post-clarification stage, and wherein the post-clarification stage incorporates a filter.
There are known to the art an entire spate of installations for the mechanical-biological purification of waste water or sewage, which, however, in consideration of the ever increasing requirements concerning the purification capacity or output are associated with certain drawbacks.
With known installations, the biological stages of which incorporate immersion drip bodies or drip or trickle bodies, the waste water is initially mechanically pre-clarified in a preclarification stage and then enters the biological stage. In the case of installations operating with immersion drip bodies the micro-organisms appear in the form of a biological mat upon the rotating immersion drip bodies. The micro-organisms acquire the oxygen necessary for decomposition of the sludge material due to rotation of the immersion drip body which ensures a continuous emersion and immersion of the micro-organisms into the water. In a post-clarification stage which follows the biological stage the biologically purified waste water or sewage is separated from the entrained floating particles which, in the first instance, consist of the biological mat, the so-called activated sludge, which has dropped-off the immersion drip body. Separation occurs by settling of the floating particles. Installations incorporating drip bodies function in an analogous manner, with the exception that the biological mat is formed in a loose pile at the bodies which are located in the atomsphere and over which there is continuously poured the waste water to be purified. What is disadvantageous with such installations is not only the fact that there is required a relatively large post-clarification basin in order to settle or quiet the biologically purified waste water to such an extent that the floating particles can settle, but there is continually present the danger that with hydraulic overloading of the installation such floating particles can be delivered to the outlet together with the purified waste water.
With the heretofore known total oxidation installation, the waste water, as a general rule, without any previous treatment in a pre-clarification stage, is introduced directly into an aeration vessel, generally after passage through a squeezing mill. The activated sludge in the aeration vessel ensures the biological decomposition of the sludge material, and the activated sludge receives the oxygen required for the decomposition process through intensive blowing-in of air into the basin or as a result of the circulation. The thus biologically purified waste water must be freed from the floating particles in a post-clarification stage. In this type of installation particular difficulties are present in overcoming the problem of the floating particles, since due to intensive aeration air bubbles collect at the floating particles which again, in the first instance, consist of activated sludge and therefore render difficult the settling process in the post-clarification stage. Hence, oftentimes there is arranged a degasification stage in front of the post-clarification stage. The danger of entraining floating particles, that is to say activated sludge, from the biological stage is essentially even further increased during sudden hydraulic loading of the total oxidation installation, so that with this type of installation there is present the considerable danger that the floating particles will arrive at the outlet for the clarified waste water or sewage.
The known activated sludge installations operate similar to the total oxidation installations, however require shorter aeration times. Additionally, in this case the prevailing waste water or sewage is not conducted through squeezing mills, rather, as a general rule, is pre-clarified in pre-clarification stages, then introduced into the biological stage. Such consists of a large basin in which the waste water is brought into contact with the activated sludge, and through intensive circulation of the basin contents and by blowing-in air is likewise aerated. Also in this case there are present the difficulties which were previously mentioned in conjunction with the total oxidation installations.
The activated sludge installation according to Swiss patent 485,605 strives to avoid the aforementioned drawbacks in that it contemplates that the biological stage is a receiving vessel or container sub-divided into at least two compartments by a filter formed of plastic or glass fibers. The waste water infeed opens into one compartment and the other compartment is connected with the outlet for the clarified waste water. With this known installation the settling basin, previously employed as the post-clarification stage, is replaced by a filter. However, in practice considerable difficulties arise during operation of the installation since the filter becomes easily clogged by the floating particles, so that there is lost the permeability of the filter needed for the functional reliability of the installation. The biologically purified waste water of the biological stage then arrives via the provided safety overflow together with the floating particles, especially the activated sludge, at the outlet. Such installations only can be employed with small sudden hydraulic loads.